Superfinishing is a process used to remove small amounts of stock from a workpiece. Superfinishing is commonly performed after grinding to achieve the following objectives: removing an amorphous surface layer produced by grinding, decreasing surface roughness, improving part geometry, and providing a desired surface topography. The removal of the amorphous layer improves the wear resistance of the workpiece. The decreased surface roughness further increases the load-bearing capability of the workpiece, and the characteristic topographical pattern aids in oil retention.
Superfinishing is generally performed using a vitreous-bonded microabrasive tool formed of abrasive particles in a bond matrix. xe2x80x9cMicroabrasivexe2x80x9d tools are generally defined as abrasive tools wherein the size of the abrasive particles is 240 grit (63 micrometers or microns) or finer. Microabrasive tools are generally manufactured according to one of a couple well-established processes.
According to one process, abrasive grains and a bonding material are mixed with binders assisted by a small amount of liquid (e.g., less than 4% by weight). The liquid usually is water. This xe2x80x9csemixe2x80x9d-dry mix then is cold pressed to shape and green density. Finally, the green form is fired to produce a microabrasive tool.
Another even-older process for making microabrasive products is the so-called xe2x80x9cpuddlexe2x80x9d process. According to the puddle process, the abrasive grains and the bonding material are mixed with enough water to produce a pourable slurry. Consequently, the puddle process is considered a wet process. The slurry is poured into a mold and allowed to dry. The dried mixture is then fired to produce an abrasive tool.
One advantage of the puddle process is that by mixing the abrasive grains and the bonding material in a slurry, a better distribution of the abrasive grains and the bonding material (i.e., better mixing) can be obtained compared with what is typically obtained with dry or semi-dry mixing.
Nevertheless, in both of these forming methods, abrasive products are produced in which particles of the bonding material and the abrasive are nonuniformly dispersed. In the semi-dry process, this nonuniform dispersion is due to incomplete mixing of the bonding material and the abrasive grains. In the wet process, the nonuniformity is generally due to settling of the bonding material and the abrasive grains relative to one another.
The invention is generally directed to a method for making a microabrasive tool, and a slurry and green stage article from which the microabrasive tool is formed.
In a method of this invention, the microabrasive tool is fabricated by casting a slurry that includes a liquid, abrasive grains, a bonding material, a polymer, and at least one cross-linking agent to form a structure of a green cast article. The polymer is then ionically cross-linked within the mold, wherein the ionically cross-linked polymer fixes the structure of the green cast article.
The slurry of the invention includes a liquid, abrasive grains, a bonding material, an ionically cross-linkable polymer and at least one cross-linking agent.
The green stage article of the invention includes abrasive grains, a vitrified glass, and an ionically cross-linked polymer.
The method of this invention can be employed to manufacture microabrasive tools having improved homogeneity over products formed by conventional semi-dry-press and puddle processes. Mixing the abrasive grains and bond material in a slurry takes advantage of the more uniform distribution of components than generally obtainable by known wet processes. It does so, however, without the typical drawbacks of conventional wet processes. In the methods of this invention, the quick-setting action of the polymer fixes, or locks in, the microstructure of this homogeneous system, reducing or eliminating the tendency of nonuniform settling observed in wet processes. Consequently, the cast article has more uniform density and hardness in comparison to articles made in accordance with known methods. The improved homogeneity of the microabrasive tool promotes greater consistency, evenness and efficiency in the superfinishing performance of the microabrasive tool. Additionally, high-quality cast articles can be produced more consistently with the methods of this invention, and product reject rates consequently can be reduced. Further still, the methods of this invention are adaptable and generally are inexpensive to conduct.